Solar cells, also termed photovoltaic or PV cells, and solar modules convert sunlight into electricity. These electronic devices have been traditionally fabricated using silicon (Si) as a light-absorbing, semiconducting material in a relatively expensive production process. To make solar cells more economically viable, solar cell device architectures have been developed that can inexpensively make use of thin-film, light-absorbing semiconductor materials such as copper-indium-gallium-sulfo-di-selenide, Cu(In, Ga)(S, Se)2, also termed CIGS. This class of solar cells typically has a p-type absorber layer sandwiched between a back electrode layer and an n-type junction partner layer. The back electrode layer is often Mo, while the junction partner is often CdS. A transparent conductive oxide (TCO) such as zinc oxide doped with aluminum is formed on the junction partner layer and is typically used as a transparent electrode.
Despite the demonstrated potential of CIGS in thin-film solar cells, the toxicity and low abundance of indium and selenium are major impediments to the widespread use and acceptance of CIGS in commercial devices. An attractive alternative for absorber layers of thin film solar cells are quaternary chalcogenide, particularly copper zinc tin sulfide, Cu2ZnSnS4 (CZTS). It has a direct bandgap of about 1.5 eV and an absorption coefficient greater than 104 cm−1. In addition, CZTS does not include any toxic or nonabundant elements.
Thin films of CZTS have been prepared via sputtering of Cu, SnS, and ZnS precursors, hybrid sputtering, pulsed laser deposition, spray pyrolysis of halides and thiourea complexes, electrodeposition/thermal sulfurization, E-beam Cu/Zn/Sn/thermal sulfurization, and sol-gel deposition, followed by thermal sulfurization.
Bulk quantities of CZTS have been prepared in evacuated quartz ampoules at temperatures between 400° C. to 1150° C. Bulk quantities have also been prepared in a furnace with a source of sulfur, such as H2S.
There is a need for a safe, robust process to produce CZTS in bulk quantities for non-vacuum based thin-film photovoltaics.